Loudspeaker with flat frequency characteristics

ABSTRACT

A plurality of sound passages connect cavities on both sides of the edge portion of the diaphragm in a horn type loudspeaker, the passages having a length less than the half-wave of the high reproduction threshold frequency of the loudspeaker.

United States' Patent [191 Maekawa et al.

[4 1 Feb. 18,1975

1 1 LOUDSPEAKER WITH FLAT FREQUENCY CHARACTERISTICS [75] Inventors: Kouji Maekawa; Yutaka Tamura,

both of Tokorozawa, Japan [73] Assignee: Pioneer Electronic Corporation,.

Tokyo, Japan [22] Filed: Oct. 19, 1972 [21] Appl. No.: 298,907

[30] Foreign Application Priority Data [58] Field of Search 179/1155 R, 115.5 H, 180, 179/1155 ES; 181/27 R, 31 R, 152, 159,

[56] References Cited UNITED STATES PATENTS 1,930,915 10/1933 Wente 181/27 R Primary ExaminerKath1een H. Claffy Assistant Examiner-George G. Stellar Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A plurality of sound passages connect cavities on both sides of the edge portion of the diaphragm in a horn type loudspeaker, the passages having a length less than the half-wave of the high reproduction threshold frequency of the loudspeaker.

3 Claims, 4 Drawing Figures msw 7. 586 Pmmiu 3.86

I SHEET 1 [1F 2 FIG. I (PRIOR R WV m W M v FREQUENCY FIG.

umzommwm FREQUENCY PATENTEU FEB 1 81975 SHEET 2 BF 2 LOUDSPEAKER WITH FLAT FREQUENCY CHARACTERISTICS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in loudspeakers of the horn and dome types, and more particularly, to an arrangement for providing a flat frequency characteristic for the same.

2. Description of the Prior Art Conventionally, in the design of the driving portion for a horn type loudspeaker or the like, the greatest difficulty occurs in the design of this element of the structure. The problems in the design involve the prevention of resonance at the edge portion of the diaphragm which constitutes the driving source for the speaker and the obtaining sound radiating from the diaphragm nozzle in phase with the sound radiating from the peripheral edge portion of the diaphragm.

In a loudspeaker construction in which no compensation is provided on or near the edge portion, the sound radiated from the edge (or a large sound pressure caused by resonance at the edge of the diaphragm), disturbs the sound which is reproduced by the diaphragm and radiated from the nozzle (mainly dip caused by phase delay). This disturbance is the reason for the attenuation which occurs over the range between 3,000 and 4,000 c/s on the frequency characteristic, a plot of the same which is shown in FIG. 1 for the prior art horn type loudspeaker.

Many attempts have been made to reduce and minimize the influence of the diaphragm edges. One attempt is to use an edge having a relatively small area, for instance, to minimize the amount of sound radiated from the edge of the diaphragm. Another attempt resides in the provision of several small holes on the portion which forms a cavity above the diaphragm edge and the filling of the holes with materials which absorb the sound pressure developed by the edge. A' third attempt is to provide many small holes within the edge itself. The first attempt, however, has such defects that the choice of materials is difficult for use in small diaphragms and diaphragms having a relatively limp edge, the assembly procedures are structurally difficult and a large percentage of sound of the third harmonic wave is generated because of the bad lineality of the device. The second attempt has such defects that an unbalance between the up and down motions causes a distortion, because the conditions are different between the upper and lower surface portions of the edge of the diaphragm. The third approach has such defects that it is a difficult task to perforate the corrugated portion of the diaphragm edge with relatively small holes and, in addition, the provision of the small holes reduces the intensity of vibration. Thus, any approach suggested by the prior art is unacceptable.

SUMMARY OF THE INVENTION The present invention improves horn or dome type loudspeakers without the occurrence of the above defects and, therefore, it is accordingly a primary object of this invention to provide a loudspeaker with a flat frequency characteristic over the full sound range. This is achieved in the present invention by coupling the cavities occurring above and below the edge of the diaphragm so that the sound pressures on the upper and lower surfaces of the edge are canceled.

Another object of the present invention is to provide a loudspeaker which is capable of improving the various characteristics. This is based on the fact that the acoustical load condition remains constant irrespective of the loading of sound absorption material on and around the sound passage.

A further object of this invention is to provide a loudspeaker which minimizes the distortion, especially in the lower frequencies. This is achieved by using sound passages whose length is less than a half-wave of the high reproduction threshold frequency. Therefore, approximately equal sound pressures occur at the upper and lower surfaces of the edge and permit the edge to move up and down easily, so that the upward and downward deviation of the edge of the diaphragm will be equal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph of the frequency characteristic of a conventional horn type loudspeaker.

FIG. 2 is a graph of the frequency characteristic of a horn type loudspeaker of the type incorporating the present invention.

FIG. 3 is a cross sectional view of one embodiment of a horn type loudspeaker in accordance with the present invention.

FIG. 4 is a cross sectional view of a portion of a loudspeaker incorporating the invention and forming an alternative embodiment of the same.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference to the drawings, like elements are given like numerical designations in both embodiments. In FIG. 3, for instance, a loudspeaker in accordance with the present invention comprises a yoke 1 having a magnet 2 fixed at the center of the same, and a pole 3 fixed to the top surface of the magnet. An annular plate 4 concentrically surrounds the magnet and forms a gap therebetween, the construction as so far described being conventional. To such a loudspeaker, the following structures are added. A horn 5 (with a throat piece 9) is provided, the bottom of which forms a concavity 51 or ring groove, in this case, in conjunction with the upper surface of the annular plate 4. A pair of gaskets 6 are fixedly positioned within the concavity 51 of horn 5 and plate 4 and support the edge 71 of a diaphragm 7 by sandwiching the edge therebetween. A voice coil 8 is fastened to an annular projection at the bottom of the diaphragm 7, the coil being positioned within the gap between the magnet pole 3 and the annular plate 4 and moving axially of the pole and magnet in conventional fashion. It is noted that the concavity 51 is divided by the edge 71 of the diaphragm into upper and lower cavities respectively.

According to the present invention, several small holes, as at 61, for the upper annular gasket 6, and 71a for the lower annular gasket 6, the holes 61 and 71av being in alignment at circumferentially spaced positions so as to form sound passages which couple the upper and lower cavities. The length of each sound passage is formed such that it is less than the half-wave length of the high reproduction threshold frequency of the speaker.

Reference to FIG. 4 shows an alternate embodiment of the present invention, in which the concavity 51 is formed entirely within the cover formed by the lower portion of the horn 5 and overlying the annular plate 4, the concavity being axially enlarged in the area of reception of the inner end of the diaphragm edge 71, and in which case, the upper and lower gaskets 6 are attached to the cavity wall only at the outer sidewall of the same. However, as in the case of the prior embodiment, each of the aligned holes 61 and 71a are of a combined length so as to form a sound passage with a length less than the half-wave of the high reproduction threshold frequency of the speaker. Conventional means fix the gasket 6 to the outside sidewall of the concavity 51 and also fix the annular gasket 6 to each side of the diaphragm edge 71, such means taking the form of adhesive of the like.

The operation of the invention in both embodiment forms is similar. Since the cavity above the edge 71 of the diaphragm is coupled with the cavity below it through a plurality of sound passages having a length less than a half-wave of the high reproduction threshold frequency, the sound pressure which has developed by the vibration of the diaphragm 7 and acts on the upper and lower surfaces of the diaphragm edge 71, cancel each other. Therefore, a sudden attenuation in freuqency characteristic over the range between 3,000 and 4,000 c/s as in a conventional speaker of this type, will not occur, as readily evidenced by reference to FIG. 2, which shows a flat characteristic as being obtained in a device such as that shown in FIGS. 3 or 4. The improvement of various characteristics are also possible, since it is easy to insert sound absorption material (not shown) in the sound passages formed by holes 61 and 710.

This invention is not confined to the above embodiments but effective applications will be found in horn speakers including cone speakers or in dome speakers.

As mentioned above, the expected result can be obtained by this invention for the reasons described below, as well as other reasons.

Since the loudspeaker of the invention is a horn or dome type of loudspeaker with a diaphragm whose edge portion is such as to have a cover overlying its front surface, and having cavities above and below the edge portion which are coupled together through several sound passages with the length of the sound passage being less than the high reproduction threshold frequency, the sound pressures exerted on the upper and lower surfaces at the edge of the diaphragm are canceled. That is, the sound pressure developed by the edge wont affect the sound pressure developed by the center of the diaphragm, therefore, the attenuation on the frequency characteristic does not occur, and a flat characteristic is thus obtained.

in addition, the construction of the loudspeaker of this invention minimizes the difference of sound pressures between the upper and lower surface, and particularly, at the edge, and permits the edge to vibrate freely and in an axial direction and makes the axial deviation equal so as to prevent distortion.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in'the art that the foregoing and other changes in form and details may be made therein without departing from the spirit, and scope of the invention.

What is claimed is:

l. in a loudspeaker construction forming'a horn type speaker or the like and including; a casing having an annular plate concentrically surrounding a circular magnet and forming an annular air gap therebetween, a diaphragm having a central portion overlying said magnet, a cylindrical voice coil support extending from the side of the diaphragm facing the magnet and concentrically carried within said annular gap, and an integral peripheral edge portion of the diaphragm overlying said annular plate, a cover overlying the side of said diaphragm not facing the magnet, the improvement comprising: means including at least said cover defining an annular cavity receiving the peripheral edge onlyof said diaphragm, means for fixing said diaphragm to said casing solely at its peripheral edge with said peripheral edge portion dividing said cavity into two portions on either side thereof of equal size comprising a pair of annular gaskets which sandwich the peripheral edge of the diaphragm and a plurality of holes are provided at circumferentially spaced positions within said gaskets in axial alignment with themselves and with corresponding holes within the peripheral edge of the diaphragm to form a plurality of short length sound passages within the peripheral edge of said diaphragm di rectly connecting said cavity portions with said passages having a length less than the half wave of the high reproduction threshhold frequency of the loudspeaker.

2. The loudspeaker construction as claimed in claim 1, wherein: said cover and said annular plate define said cavity and sandwich a portion of said pair of annular gaskets and the peripheral edge of the diaphragm therebetween.

3. The loudspeaker construction as claimed in claim 1, wherein: said cover alone includes an annular concavity having an axially enlarged portion remote from said voice coil support forming said cavity and wherein said sandwich is fixed to the outer sidewall of the axially enlarged annual concavity alone. 

1. In a loudspeaker construction forming a horn type speaker or the like and including; a casing having an annular plate concentrically surrounding a circular magnet and forming an annular air gap therebetween, a diaphragm having a central portion overlying said magnet, a cylindrical voice coil support extending from the side of the diaphragm facing the magnet and concentrically carried within said annular gap, and an integral peripheral edge portion of the diaphragm overlying said annular plate, a cover overlying the side of said diaphragm not facing the magnet, the improvement comprising: means including at least said cover defining an annular cavity receiving the peripheral edge only of said diaphragm, means for fixing said diaphragm to said casing solely at its peripheral edge with said peripheral edge portion dividing said cavity into two portions on either side thereof of equal size comprising a pair of annular gaskets which sandwich the peripheral edge of the diaphragm and a plurality of holes are provided at circumferentially spaced positions within said gaskets in axial alignment with themselves and with corresponding holes within the peripheral edge of The diaphragm to form a plurality of short length sound passages within the peripheral edge of said diaphragm directly connecting said cavity portions with said passages having a length less than the half wave of the high reproduction threshhold frequency of the loudspeaker.
 2. The loudspeaker construction as claimed in claim 1, wherein: said cover and said annular plate define said cavity and sandwich a portion of said pair of annular gaskets and the peripheral edge of the diaphragm therebetween.
 3. The loudspeaker construction as claimed in claim 1, wherein: said cover alone includes an annular concavity having an axially enlarged portion remote from said voice coil support forming said cavity and wherein said sandwich is fixed to the outer sidewall of the axially enlarged annual concavity alone. 